Multiple-chip probe and universal tester contact assemblage

ABSTRACT

A probe card assemblage for simultaneously testing one or more integrated circuit chips including an interposer having on one surface a plurality of protruding contact elements for electrically contacting one or more chips of a wafer positioned atop a layer of compliant material, and arrayed in a pattern corresponding to a chip pads, a series of conductive vias through the electrically insulating interposer which connect the chip contact elements with an arrangement of leads terminating in a universal arrangement of connectors on the second surface, and a probe card with connectors mating to those on the interposer. The connectors on the interposer is secured are secured to those on the probe card, thereby providing a vertical probe assemblage which makes use of ultrasonic energy to minimize scrub or over travel. The universal probe card is specific to a tester configuration and common to a family of circuits to be tested.

This is a divisional application of co-pending application Ser. No.09/915,919 filed Jul. 26, 2001, which claims the benefit of provisionalapplication Ser. No. 60/228,070 filed Aug. 24, 2000, the contents ofwhich are herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to the testing of integrated circuits, and moreparticularly to a probe card apparatus for simultaneously testingmultiple integrated circuit chips.

DESCRIPTION OF PRIOR ART

Integrated circuits (ICs) are formed as multiple, identical, discretechips on a semiconductor crystal wafer. Each of the integrated circuitchips is usually tested to determine whether or not it functions asintended prior to cutting the semiconductor wafer into individual chips.Typically, the chins are tested by computer operated test apparatus thatexercises the circuits on the chips, using a testing process commonlyreferred to as multiprobe testing.

Conventional multiprobe testing employs a probe card which includes aplurality of electrical leads terminating in needles, which in turn makecontact with input/output contacts of the various circuit elements on anintegrated circuit chip under test. The chip contacts most often are thepads to be electrically connected to the next level of circuitry, andare called bond pads. In prior art, it is typical for probe cards to bebuilt by attaching metal needles, such as tungsten or tungsten-rheniumto conductive traces on a polymeric ring. The needles or probe elementsmay be secured to the ring by an adhesive or they may be bonded, as bywelding to a blade. An opening is provided in the center of the ring forthe needles to extend through, and for aligning the needles to the bondpads on a chip. The card is positioned in a probe head which provideselectrical connection to the controlling computer, and whichmechanically brings the needles into contact with the bond pads on thechip.

The needles must all fall in the same place in order to assure that eachone makes electrical contact with a specific input/output contact orbond pad on the integrated circuit. This is accomplished by bending theneedles after they are mounted on the probe card, which is laborious,time consuming, and expensive. Even after such adjustment, the needlescreep back into their original positions, or are moved by pressure ofthe needles against the chips resulting largely from a scrubbing actionused to assure penetration of any oxide coating or contamination on thebond pads.

However, the close spacing necessary for testing some chips cannot beachieved with conventional needle contacts. The tight pitch of probeneedles and the angles of their projection are extremely difficult tomanufacture, and in turn insures a high cost. Further, maintenance ofsuch cards adds significantly to the cycle time of testing. As a resultof these issues, a number of attempts have been made to providealternate probe card technology. Much of the newer technology oftencenters around thin film photolithographically defined conductor leadson polymeric membranes with plated or spring loaded contact mechanisms.Photolithographic definition of the leads adds cost to the testingprocedure, not only as a result of the initial cost and multiple stepsinvolved, but also because new artwork and masks are required for eachnew device and/or change, thus adding to cycle time for production. Eachof these approaches must have a means for applying uniform pressure tocause the membrane to make uniform contact across the chip. The issue ofuniform contact, as well as alignment is aggravated by thermal expansionof the membrane because very often the chip generates a significantamount of heat during the testing procedure.

Further, with multiple touch downs and heat, probe tips become oxidized,and may require cleaning or replacement, thus adding to the test time.Recent developments in probe tip technology have demonstrated that noblemetals do not suffer from oxidation mechanisms as do tungsten andrhenium, and as a result have a more stable contact resistance. Broz, J.J., and Rincon, R., EE—Evaluation Engineering, September, 1999 and Broz,J. J., et al “Probe Contact Resistance Variations During ElevatedTemperature Wafer Test”, Proceedings of the 30^(th) IEEE—InternationalTest Conference, Atlantic City, N.J., PP 396–405, September 1999.

However, the biggest wafer testing issue may be that of long test time.Each chip is tested sequentially, requiring realigning and repositioningthe probes for each touch down. Testing complexity, and the timerequired varies with the circuitry, but the alignment and positioningtime may equal or exceed that of the testing itself.

Further, the size of semiconductor wafers has increased, and thegeometry of circuitry has decreased, resulting in an increase in thenumber of chips per wafer. There are multiple wafers in a productionlot, and with the increased test time per wafer, processing of a lotthrough wafer fabrication may require less time than testing.Consequently, test time resulting in product delivery delays, as well asthe cost associated with expensive tester utilization has become a verysignificant issue to the industry.

Because of the aforementioned issues with prior wafer probetechnologies, and because of the anticipation of even more test timeissues and tighter pitch of bond pads on integrated circuits of thefuture, it would be very advantageous to the industry to have a probeapparatus capable of significantly decreasing test time, and a means ofrapidly fabricating such a device with a high density of robustcontacts.

SUMMARY OF THE INVENTION

It is an object of the current invention to provide a wafer probe cardassembly for testing one or more integrated circuits simultaneously,thereby significantly decreasing the time required to test a wafer.

It is an object of the invention to provide a probe card assemblagecapable of making electrical contact between a high density of chipinput/output contact pads, and a probe card connected to an integratedcircuit (IC) tester.

It is further an object of the invention to provide a means forelectrical contact between the chip contact pads, and a probe cardhaving universal or standardized connections for a family of integratedcircuit devices to be tested.

It is another object of the invention to provide a probe card contactapparatus which can be manufactured rapidly and economically.

It is yet another object of the invention to provide a probe cardapparatus having a thermal expansion coefficient similar to that of thesemiconductor device to be tested so that contact is not compromised asa result of chip heating during testing.

Yet another object of the current invention is to provide a reliable,high performance probe card contact apparatus.

The objectives of this invention are met by providing a probe assemblagefor wafer testing including an interposer having on one surface aplurality of protruding contact elements in an arrangement correspondingto a pattern for electrically contacting one or more chips of a wafer,conductive vias through the electrically insulating interposer whichconnect the chip contact elements with an arrangement of contact pads onthe second surface, and a probe card with mating contacts. Conductivetraces on the second surface of the interposer are routed from the viasto terminate in a connector positioned in a universal or standardizedpattern. The contact elements on one or both surfaces are positionedatop a compliant material in order to allow sufficient pressure to beapplied for good electrical connection. The interposer is secured to aprobe card having a plurality of connectors corresponding to those onthe second surface of the interposer. The universal or standardizedpattern on the probe card is specific to a tester configuration, and iscommon to a family of circuits to be tested, thereby providing asignificant reduction in probe card inventory, cost avoidance, andinstallation time.

The probe contact elements and interposer are designed to test one ormore contiguous chips simultaneously. The array is preferably no morethan two chips deep so that the leads may be fanned out, and align withprobe card contacts. Manufacturing capability of probe cards typicallydoes not provide very high density contacts, as does that for integratedcircuits.

High density chip contact elements are fabricated as protrudingstructures, such as a stud bump or micro-wire of a noble ornon-oxidizing metal, and are positioned atop a compliant material, andconnected to a conductive via in the interposer.

On the second surface of the interposer, the via terminates in aconductive pad which is subsequent routed to a connector element. Viasare formed either directly through the interposer, and/or steppedhorizontally in order to fan out from the tightly spaced chip contacts,and provide more generously spaced second contacts. The interposer mayinclude one or more buried metal planes as ground or other performanceenhancements, and may be contacted by selected vias.

The interposer is securely attached to a universal probe card havingconnectors mated to those on the interposer. The probe card contactpattern is universal or standardized to a family integrated circuitdevice types, and to a particular tester.

Alternately, for single chip testing applications, the interposer havingat least one compliant surfaces under the connectors and havingcontoured edges is snapped or press fit into the universal probe cardproviding a low cost, robust chip contact assemblage.

The foregoing and other objectives, features and advantages will becomemore apparent from the following detailed description of preferredembodiments of the invention which proceeds with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of an assemblage for testing an array of “y”×2chips, including an interposer with contact elements and a probe card.

FIG. 2 is a cross section of an interposer having chip contact elementson one surface, and connection elements to a probe card on the secondsurface.

FIG. 3 is a cross section of a portion of a probe interposer with viasconnecting chip contact elements to probe card connectors and pads.

FIG. 4 is an example of the second surface of an interposer with tracesto a universal connector pattern.

FIG. 5 is a detailed section of an interposer and card assemblage.

FIG. 6 is a cross section of a single chip interposer for press fit to aprobe card.

FIG. 7 a is a robust single chip test probe interposer with edgeconnections.

FIGS. 7 b and 7 c are top and bottom views of a single chip test probeinterposer with edge connections.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a multiple-chip probe assemblage 100 in accordance with thepresent invention. The assemblage 100 includes an interposer 10 havingcontact elements 21 for testing two (2) or more integrated circuit chipson a semiconductor wafer 1, a probe card 50 having universal orstandardized contacts, and a means 30 to secure the interposer 10 to theprobe card 50. The multiple-chip probe assemblage 100 is suitable forwafer testing at elevated temperatures. During testing of the chip siteson a wafer 1, the multiple-chip probe assemblage provides a means forcontacting the input/output pads on the chips, and connecting withcorresponding pads on a probe card 50 attached to a testing apparatus(not shown). The interposer of the multiple-chip probe assemblageminimizes adverse effects of thermal coefficient of expansionmismatches.

FIG. 2 provides a more detailed view of the interposer having contactelements on both of the major surfaces. A plurality of chip contactelements 21 protrude from the first surface 111 of the interposer 10,and a plurality of connectors 22 for electrically contacting the probecard are arrayed on the second surface 112. The chip contact elements 21are positioned to mirror the input/output pads of one or more integratedcircuit under test (not shown).

Chip contact elements 21 include a noble or non-oxidizing metalprotrusion, such as a stud bump 24 seated on a metal pad 23 which is inturn positioned atop a compliant material 27. The terms noble ornon-oxidizing metal are used to include those metals which may form athin film of oxide, which is self limiting and is readily pierced byminimal contact force.

The compliant material 27 having a relatively low modulus of elasticityis recessed into the interposer under the contact element to absorbstress as contact to the chip pad is applied and thus avoid damage toeither surface. A conductive via (not shown) extends through thecompliant material. Alternately, in FIG. 3, the compliant material maybe a film 33 across the surface of the having the metal pads and contactelements atop the film, and a via through the film. The protrudingelements are preferably formed as stud bumps 24 attached by mechanical,or ultrasonic bonding equipment, similar as that used for wire bondingsemiconductor devices. Stud bumping is a term applied to a metallic ballformed by a wire bonder, wherein the ball is welded to a pad, the excesswire removed and the protrusion coined or otherwise partially flattenedto control the “z” axis dimension. Alternately, the chip contactelements are plated microspring wires, or other types of metallicprotrusions attached to a metallized pad 24. Microspring wirestechnology is commercially available from Precision Art Coordinators, 22Almeida Avenue, East Providence, R.I. 02914.

Use of non-oxidizing metal, or metal with self limiting oxidation probeshas been shown to minimize the amount of scrubbing or over-travelrequired to make good electrical contact to aluminum or copper bond padson integrated circuit chips. (Broz, J. J. and Rincon, Rey “Probe ContactResistance Variations During Elevated Temperature Wafer Test”,Proceedings of the International Test conference, September 1999,Atlantic City, N.J., pp 396–405.)

Patterning the pads 23 for contact elements are made by photolithographyand/or laser ablation. Those features greater than 100 microns will bepatterned by the photolithographic processes typically used in printedcircuit and flex film technology, whereas those finer features will beeither totally or partially patterned by laser ablation of unwantedmetal. Software input of the design to a computer controlled fine beamlaser which ablates excess metal from a metal coated surface of theinterposer. Metallization is preferably a layer of tin over a copperalloy, or other low resistivity metals affixed by lamination, or vapordeposition over the first surface of the interposer. Subsequent todefining the pads, a thin film of a noble metal, preferably gold, isplated to cover the metal conductors. While a combination ofphotolithography and laser ablation of a metal film is the preferredmethod for patterning pads and leads on this device, alternatives areavailable in the industry, including photolithography of thin filmmetallization and plating to a required thickness.

On the opposite surface 112, a series of connectors 22 are arrayed in apattern corresponding to universal or standardized connector pattern ona probe card. Each connector 22 includes a metal pad 26, and a connectorelement 25. The connector element is preferably a thicker metal featurecapable of a pressure contact to provide electrical connection.Alternately, the connector element is an applied stud bump or microspring connector. Connectors, pads may be positioned atop a layer ofcompliant material 28 recessed into the interposer, as was the case withchip contact elements, or alternately a compliant film 34 with vias asshown in FIG. 3. In yet another alternate embodiment, a compliantmaterial is not necessary on the probe contact side of the interposerbecause the connectors themselves absorb the stresses sufficiently toavoid damage.

The conductive connectors 22 are aligned and brought into contact withthe corresponding connector on the probe card. Mechanical mating of theconnectors provides a very low contact resistance between the matchedconnectors.

Connectors 22 are most often offset from the corresponding chip contactelement 21 in a manner which allows them to be directly aligned to auniversal connector on a probe card. Off set and fan out on theinterposer connectors 22 is accomplished both within the interposer byvias 35, and by routing of metal conductors on the surface of theinterposer or compliant film covering the interposer surface. Some orall of the vias may be straight through the interposer with all routingmade to the desired location by patterned metal conductors.

The interposer 10 is a dielectric material having a coefficient ofthermal expansion in the range of 2 to 10 PPM, approaching that of thesilicon wafer. The interposer ensures that positioning of the pluralityof chip contact elements 21 upon the contact pads of the integratedcircuit chips is maintained during thermal excursions, and as shown inFIG. 3 the interposer provides support for a plurality of vias 35electrically connecting pads 23 on the first surface 111 to those 26 onthe second surface 112. Technology for fabricating conductive vias andfine lines in organic media has become widely available, as a result ofarea array packaging, such as CSP (chip scale packages) or BGA (BallGrid Arrays), and the circuit boards necessary to accommodate suchdevices. Further, multiple metal levels and planes which support commonpower and ground connections are routinely available. These buried metallevels also allow routing to off set and fan out connections from chipcontacts 21 to connectors 22.

FIG. 4 is an example of an array of connectors 22 and leads 29 on thesecond surface 112 of an interposer 10 which provide connection for four(4) chip contacts 21 to a probe card. Leads 29 fan out from the egressof a via to the universal connector 22. In FIG. 4, it can be seen thatthere are four distinct patterns with most of the leads 29 fanned to theouter perimeter in order to allow contact by probe card connectors.

An array of apertures 31 are provided near the interposer perimeter forpreferably screw type devices to secure the interposer 10 to probe card.

While the example illustrated in FIG. 4 is a two by two (2×2) chiparray, it should be understood that the technology will be the same forother array configurations, and the number is limited largely by theability to fan out leads so that probe contact can be made. It isexpected that the arrays will be more readily accommodated in an “Y” by2 deep arrangement.

Arrangement of the universal or standardized connector pattern on theinterposer 10 to match that of a probe card is made by a combination offanning the vias in an outward direction, and by final routing of leads29 on the interposer surface 112 to the universal connectors specificlocation. Routing of leads 29 connecting the vias to connectors 22 ispreferably made by coating the interposer surface with a highlyconductive metal which can be etched chemically and by a fine beamlaser, such as tin over copper. Features which are greater than 100microns are preferably photolithographically defined using techniquescommon to printed circuit board and flex film industry with the finerfeatures laser ablated. Alternately, the metal patterns are formed bylaser ablation of the undesired metal. Electroless plating with a noblemetal protects the metal leads and pads. In yet another embodiment, theleads are formed by photolithographic patterning of a thin film metallayer, etching, and subsequently plating the metal leads to the desiredthickness.

High performance embodiments of the probe interposer are achieved byproviding ground planes within the interposer, and/or by a customizeddesign of leads wherein the dimensions are designed to provide orapproach a specific impedance level.

FIG. 5 is a cross section of a representative portion a probe cardassemblage 100, including an interposer 10 with chip contact elements 21atop a recessed compliant layer 27 on one surface, vias 35 connectingthe chip contacts 21 to probe card connectors 22 on the second surface,and a probe card 50 with mating connectors 51 which correspond to thoseon the interposer.

The probe card 50 of the current invention, fabricated on a printedwiring board structure makes use of technology currently availablethroughout the probe card industry. The universal probe card 50 includesvias 53 to provide electrical connection between universal connectors 51to the interposer, and conductive traces 54 on the opposite surface ofthe probe card. Metal traces 54 on the upper surface are conductors towhich connections to the test equipment are made.

Connectors 51 on the probe card and those 22 on the interposer arearrayed in a universal or standardized pattern for a plurality ofcircuits to be tested. The location of connectors 51 on the cardcorrespond with the connectors 22 on the interposer. A probe card withuniversal connectors allows a number of devices to be tested using thesame card, by changing only the interposer with specific chip contacts.The universal probe card is specific to a particular type of testequipment.

Major components of the probe card assemblage, i.e., the interposer 10,and the probe card 50 are securely held by a series of fasteners, suchas threaded screws 30 located near the perimeter of the interposer whichprovide a mechanical force between the connectors 22 on the interposerand the mating probe card connector 51. Alternately, the probe card andinterposer can be secured together by a mechanical locking mechanism,such as a cam ring. The secure mechanical contact between connectorsresults in electrical connection between the components.

The probe card assemblage 100 functions by attaching an interposer 10with standardized probe connectors 22 to a probe card 50 having matingconnectors 51. Chip contact elements on the assemblage are aligned tothe input/output pads of one or more chips a semiconductor wafer by useof microscopes with vision in both the up and down directions, prior tobring the probe head into contact. The probe card is connected to anappropriate tester by conventional connections. Application ofultrasonic pulses provides a means to erode surface oxide orcontamination from the pads and contact elements so that the verticallyoriented, robust chip contact elements of the probe assemblage makeintimate contact to the chip pads without the need for excessive x-ymotion, and therefore minimize damage to thin, fragile bond pads on ICs.Technology for ultrasonic abrasion has been previously disclosed in U.S.patent application Ser. No. 09/443,033, filed Nov. 18, 1999, and whichis appended herein by reference.

The preferred embodiment of the probe card assemblage has been describedand illustrated for multiple chip testing. However, the technology isapplicable to single chip testing; the embodiment shown in FIG. 6includes an interposer 60 with conductive vias 68 connecting chipcontact elements 61 atop a compliant layer 67 on the first surface to auniversal or standardized array of connectors 62 on the second surface.The interposer 60 is attached to a probe card (not shown) having anarray of corresponding connectors. In one embodiment, the interposer ismechanically attached to the probe card by a threaded element, such as amachine screw recessed into the interposer, as illustrated in FIG. 5. Inan alternate embodiment, the interposer having contoured edges, as shownin FIG. 6 is attached to the probe card by being positioned in anaperture or groove designed to correspond to the interposer size andshape and is press fit to make contact.

In yet another embodiment illustrated in FIG. 7 a, a probe assemblageincludes an array of robust chip contact elements 71 not unlike thosepreviously described, attached to a series of conductive traces 75formed on a compliant film 74, which in turn is secured to theinterposer 70. Each trace forms a continuous lead following the verticalcontour of the interposer, and connecting to a connector 72 on thesecond surface 712. The connectors 72 are arrayed in a patterncorresponding with an array of universal connectors on a probe card. Theinterposer 70 with contoured edges snaps, or is press fit into a probecard (not shown). Preferably, the metal traces 75 are formed bypatterning and etching, coupled with laser ablation of a highlyconductive, ductile metal, such as copper. FIGS. 7 b and 7 c illustratesthe first 711 and second surface 712 respectively of the interposer withchip contact elements 71, probe card connectors 72, and connecting metaltraces 75.

The robust chip contact elements of each of the embodiments describedare applicable to full chip testing of the input/output pads on a chipor chips, as well as to testing process control or other test structuresplaced in scribe lines on the semiconductor wafer.

The probe assemblage of the current invention is fabricated by combiningindividual process steps known through out the industry. While apreferred method includes the following series of steps, the inventionis in no way limited to this combination, but may include alternativesand modifications as known in the industry.

The assemblage for providing simultaneous probe contact between one ofmore integrated circuit chips to a test equipment is preferablyfabricated by (a) providing an dielectric interposer having thermalexpansion characteristics similar to that of silicon, which includes aplurality of conductive vias arrayed to correspond to the pitch of chipcontact pads, and which extend from the first major surface to thesecond major surface of the interposer, (b) providing a compliantmaterial under the position of chip contact elements, {c} depositing alayer of highly conductive metal on each major surface, {d} patterningand etching the conductor designs greater than 100 microns, (e) laserablating the conductors less than about 100 microns, as well as excessunetched metal on both surfaces, (f) bonding a chip contact element toeach patterned contact pad on the first surface, and a connector elementon the terminal of each lead on the second surface, (g) providing aprobe card having a mating connector to that on said interposer, and (h)aligning said connectors, and locking or screwing the major componentsto provide electrical contact. Conductor patterns formed in step (d) ande) include on the first surface an array of pads corresponding to chipcontact pads on the first surface, and any necessary conductive leads tovias, and on the second surface an array of pads at the via egress pointand an array of conductive leads terminating in a standardized patternof pads for connectors.

The current invention provides a number of innovative advantages to thesemiconductor industry. Testing multiple chips simultaneously has asignificant impact on cycle time for device completion, and on expensivetest equipment time. Robust, and dense contact elements on theinterposer lower the cost of and lessen maintenance on probe contacts,and the method of manufacture lends itself to relatively low cost andrapid cycle time, necessary to respond to the fast paced introduction ofchip designs for both new and revised products. Software input of thecritical pad location and dimensions are based precisely on that of thechip design, and use of noble metal contacts minimizes the amount ofscrubbing or over-travel required to break oxides on the aluminum bondpass and to make excellent electrical contact. The use of ultrasonicenergy effectively allows vertical contact with minimal scrubbing, afeature necessary for testing multiple chips simultaneously. Theuniversal probe card usable for multiple circuits with connectors matingto those on the interposer provides a reduction in set-up time, and inthe cost of probe cards.

While the invention has been described with reference to specificembodiments, it is not intended to limit the scope to a particular formset forth, but on the contrary, it is intended to cover alternatives,modifications, and equivalents as may be included within the spirit ofthe invention described by the appended claims.

1. A probe assemblage for providing electrical connection between anintegrated circuit chip on a semiconductor wafer and a circuit testequipment, said assemblage including: an interposer comprising adielectric material having two major surfaces and contoured sides of theinterposer, a plurality of protruding contact elements positioned atop acompliant material on one major surface of said interposer, each elementcorresponding to a test pads on the chip, a plurality of conductive viasconnecting each of said contact elements to a metallized pad and astandardized array of connectors on the second surface of saidinterposer, a probe card having an array of connectors corresponding tosaid standardized contact array, and means attaching said probe card tosaid interposer.
 2. An assemblage as in claim 1 wherein said means toattach the probe card and interposer is by press fit.
 3. A probeassemblage for providing electrical connection between an integratedcircuit chip on a semiconductor wafer and a circuit test equipment, saidassemblage including: an interposer comprising a dielectric materialhaving two major surfaces and contoured sides of said interposer and, aplurality of protruding contact elements positioned atop a compliantmaterial on one major surface of said interposer corresponding to testpads on the chip, a plurality of conductive leads connecting each ofsaid contact elements to a metallized pad and a standardized array ofconnectors on the second surface of said interposer, a probe card havingan array of connectors corresponding to said standardized connectorarray, and said interposer is press fit into said probe card.
 4. A testprobe assemblage for simultaneously providing electrical connectionbetween scribe line test structures on one or more integrated circuitson a semiconductor wafer and an electrical test equipment, saidassemblage including: an interposer comprising a dielectric materialhaving two major surfaces, a plurality of protruding contact elementspositioned atop a compliant material on one major surface of saidinterposer corresponding to test pads on one or more integratedcircuits, a plurality of conductive vias connecting each of said contactelements to a metallized pad on the second surface of said interposer, aplurality of leads fanning outward from said pads to a standardizedarray of connectors, a probe card having an array of connectorscorresponding to said standardized contact array, and a means to attachsaid probe card to said interposer.